WPC  2"B Z`XArial ItalicArialArial BoldHP LaserJet 4 PlusIIHPLA4PLU.PRS2xCQ\'sZX#|9ND,C2xjAG;X1mC9,  Xm2PG;XP/qC:,cXq2pPG;X2n T|TOO "4^DDV6OOYAOAADDAwDADn6wD66w6RwDwwwuR?ROAnOOODOOOOOOuOAwCCCCCCCCwwwwwwA6AAA6AAgww6A6[6RRRwwwwTDDwuuu6RwDwwDu414WddddddddddddddddddddddddddddddddddddddddNTT~PYVPTO33PPPPTTyuu3OuO"uu~uu"m+^99Ipp.DDNt9D99pppppppppp99tttp̅}9ep}}999\p.ppepp9pp..e.ppppDe9peeeeE5EtD9sZDDD9DDDDDDpD|9pppppȰepppp99999999pppppppppepp|pepppppeeee|pppppppppppp9.999.99Xeep.p:p.pDp.pxppppȼDDDeeee}L}9}9ppppppe}e}e}epp.pDe}9ee|pp8dp,(,WddddddddddddddddddddddddddddddddddddddddNHxxHlpD|pppppLJpDHpD,,DDpDDxppxHxxHsdd,DdD"dxdldtxxd"m+^:D`pp8DDLt8D88ppppppppppDDttt|Đ|8p|||D8Dtp8p|p|pD||88p8||||LpD|pppdL8LtD8ttDDD8DDDDDDpD|8pppppȰppppp88888888|||||||||pp|||p||ppppppppppp||||||||88888888ppp|8|L|8|`|8|||||ȼLLLpppp|`|D|D||||||p|d|d|d||8|Lp|Dpp||:dp,0,WddddddddddddddddddddddddddddddddddddddddNHxxHppD|pppppLHpDPpD88ddpDDxppxHxxHs||8ddD"dxxldtxxd2  P  88 #Xp2PQ XP#  yx8dddy Jicarilla LaJara|'`v(#5Conceptual Design 88  HH  III.HYDROLOGIC DESIGN CRITERIA   R A.` ` Probable Maximum Flood (#` XX` ` The Probable Maximum Flood (PMF) is the maximum runoff condition resulting from the most severe combination of hydrologic and meteorologic conditions that are considered reasonably possible for the drainage basin study. The PMF for Lajara Lake was determined to have a maximum inflow of 44,716 cubic feet per second (cfs). The PMF discharge above the diversion dike was determined to be 14,275 cfs, 673 cfs of which was included in the above inflow into the lake. The remaining 13,602 cfs overtops the diversion dike.(#`  R B.` ` Inflow Design Flood(#` ` ` The Inflow Design Flood for Lajara Lake Dam is equal to 40% of the Probable Maximum Flood, 16,632 cfs. The existing spillway will pass between 20 and 25% of the PMF before overtopping of the dam occurs, assuming that the diversion dike does not fail upon overtopping. A modification to the structure must be make in order to bring the dam into regulatory compliance.(#` ` ` If all of the flow were diverted into the reservoir without overtopping the diversion dike, the present spillway would pass 25% of the PMF after routing through the reservoir. Presently, the difference between the emergency spillway crest and the top of the dam is approximately 4.1 feet. Increasing the present 20 foot spillway length, providing overtopping protection for the dam, or most likely a combination of the two would remediate the spillway deficiency.(#` ` ` Additionally, modifications to the detention dike would increase upstream(-V*V*HH detention storage. As has already been demonstrated from the detention provided by the existing detention dike, the storage volume in the upper reservoir between the spillway crest and the maximum allowable water surface elevation has a significant dampening effect on the inflow hydrograph. In other words, if the upstream dike is raised the inflow volume will be detained in the upper reservoir, lowering the peak discharge and lengthening the time base of the hydrograph. This option would require design of an upstream (detention) dike to pass the appropriate flow, but could significantly reduce the downstream spillway capacity needed.(#` XX` ` Based on the hydraulic model, the diversion dike does not pose an incremental risk to the downstream habitable structure, and hence, does not require modifications based on that criteria. Because of the immediate proximity of the dike to these structures, a control structure that would initiate breaching in a location away from the structures should be considered. The low spot in the dike is now the interface between SH 537 and the dike. Overtopping and breaching would occur there and carry the flow to the structures. A breaching spillway and channel further to the west would force any large flood wave to begin away from the structures and allow residents to access high ground east of SH 537.(#` ` ` One other improvement for protection at the dike that might be considered is increase of the diversion intake capacity. Currently, the intake is capable of passing only 5 % of the diversion drainage PMF. Replacement of the four CGMPs with five or six boxes could significantly increase capacity.(#`  R$ C.` ` Development of Conceptual Improvements(#` ` ` The primary remediation concern at Lajara Lake Dam is the inadequate spillway capacity to pass the inflow design flood. Options for improving(-V*V*HH spillway capacity are not particularly restricted by topography. However, viable options are complicated by the upstream middle dike which divides the reservoir into upper and lower lakes, and a drainage west of S.H. 537 whose flow is diverted into the Lajara Lake by a diversion dike west of S.H. 537 and through CMP culverts which cross under S.H. 537. The options are also complicated because Lajara Lake Dam is essentially parallel to S.H. 537 and the downstream toe is close to the highway which limits drainage away from the dam. Of lesser concern is the fact that the existing outlet is inoperative and abandoned.(#` ` ` Eight improvements were considered in the Feasibility Design Report to address the hydraulic concerns of Lajara Lake Dam. Two of these improvements were not recommended for further investigation in this report; (1) enlarge the existing spillway and raise the middle dike to an intermediate elevation 7336.5 and (2) add larger structures under S.H. 537 which would require raising S.H. 537.(#` ` ` Combinations of the following improvements were considered essential for one or more of the conceptual design alternatives; (1) raise the middle dike to elevation 7340.5 and improve the existing dam spillway, (2) provide roller compacted concrete protection for the downstream slope and crest to permit overtopping of the dam, (3) raise the diversion dike and construct an emergency spillway near the right abutment of the dike, and/or (4) add fusegates to the diversion dike emergency spillway. Common to all alternative are; (5) repair the existing CGMP structures under S.H. 537 and remove potential falling rock from bluff, and (6) replace the outlet works.(#` ` ` The new outlet works would be an SCS type trickle tube outlet with a low level slide gate for releases and 36 inch outlet pipe for inspectability. Spillway improvements are shown on Drawing LX223 and include a sill for protection of the spillway floor and against erosion into the embankment.